In the next year we plan to continue our investigations of the organization and expression of the mitochondrial genome in HeLa cells. The position on the genetic map of the discret poly(A)-containing RNA components and of the individual specific tRNAs species, which we have identified as products of transcription of HeLa cell mitochondrial DNA, will be determined by RNA-DNA hybridization experiments utilizing DNA fragments producted by restriction enzymes. The number and position of promoters on the heavy and light mitochondrial DNA strands will be investigated. The metabolic properties of the poly(A)-containing RNA species and their coding capacity for defined, immunologically recognizable polypeptides in cell-free extracts will be studied. The chemical basis and physiological role of the membrane attachment of mitochondrial DNA near the origin of replication, which we have recently demonstrated in HeLa cells, will be investigated. BIBLIOGRAPHIC REFERENCES: Attardi, G., F. Amalric, E. Ching, P. Costantino, R. Gelfand and D. Lynch. (1976) Information content and gene mapping of mitochondrial DNA from HeLa cells. In: The Genetic Function of Mitochondrial DNA, C. Saccone and A.M. Kroon (Eds.), pp. 37-46, North-Holland Publishing Co., Amsterdam. Attardi, G., P. Costantino, J. England, D. Lynch, W. Murphy, D. Ojala, J. Posakony, and B. Storrie. (1976) The biogenesis of mitochondria in HeLa cells: a molecular and cellular study. In: Genetics and Biogenesis of Mitochondria and Chloroplasts, p. 3-65, Ohio State University Press, Columbus, Ohio.